Production of metal using electrochemical processes involves deposition of the metal on a cathode plate. For example, in the electrowinning or electrorefining of copper, copper metal is deposited on to stainless steel cathode plates. When the deposited copper metal has grown to a desired thickness, the cathode plate is removed from the electrolysis cell and the deposited metal is stripped from the cathode plate.
Stripping of the deposited metal from the cathode plate is desirably conducted using a largely automated process in order to achieve high throughput in the stripping plant. For example, in U.S. Pat. No. 4,840,710, the entire contents of which are incorporated herein by cross-reference, a method for stripping electrically deposited copper from a cathode is described. In this method, the cathode is flexed by an amount exceeding the strength of the adhesion bond between the deposited metal and the cathode, but not exceeding the elastic limit of the cathode. This causes at least part of the deposited metal to separate from the cathode, leaving a gap between that part of the deposited metal and the cathode. The deposited metal is then stripped from the cathode by use of wedges that slide along the surface of the cathode and the deposited metal. The use of wedges to strip the metal from the cathode involves the wedge moving in an up and down motion. The wedges prise the metal away from the cathode plate such that the angle between the metal and the cathode plate is typically between 15-25 degrees. Grippers are then used to grip the metal when in this position and pivot the metal around the bottom of the cathode plate to a horizontal position. The wedges are typically much smaller than the cathode in terms of height and width, which, when used in conjunction with grippers, sometimes produce a bow at the bottom of the stripped metal. U.S. Pat. No. 4,840,710 also describes the use of gas blasting to strip the deposited metal from the cathode.
The method of U.S. Pat. No. 4,840,710 has been commercially implemented in a number of copper plants around the world and this method forms part of the ISA PROCESS™ technology commercially available from the present applicant.
When metal is deposited on cathode plates, edge strips are typically placed on the vertical edges of the cathode plates in order to prevent metal being deposited along the vertical or side edges of the cathode plates. As a result, sheets of metal are deposited on either side of the cathode plate. These sheets of metal on either side of the cathode plate are not joined to each other along their vertical edges.
In some plants, the bottom edge of the cathode plates are covered in wax or fitted with bottom strips prior to deposition of metal thereon. This prevents the deposition of metal along the bottom edge of the cathode plates and, consequently, the sheets of metal that are deposited on either side of cathode plate remain separate from each other.
In other plants, the bottom edge of the cathode plates are not waxed or fitted with bottom strips prior to deposition of metal, which results in metal also being deposited along the bottom edge of the cathode plate. The cathodes may be provided with a substantially flat bottom edge (for instance if it is not desired to break the metal deposited along the bottom edge) or, alternatively, the bottom edge may be provided with notches, grooves or the like. This last-mentioned type of cathode is designed to assist in the stripping of the metal from the cathode, as described in Australian Patent No. 768314. In that case, the cathode is designed for the electro-depositing of a metal thereon. The cathode is designed with a groove on the bottom thereof, with metal being deposited thereon to form a frangible portion. The groove is shaped so that a line of weakness is formed in the metal deposited within the groove, such that separation of the two sheets of deposited metal is initiated upon the line of weakness. In these plants, the sheets of deposited metal on either side of the cathode plate are connected to each other by the metal that is deposited along the bottom edge. During stripping of cathodes in which metal is deposited along the bottom edge as well as on either side of the cathode plate, the wedges push the sheets of metal away from the sides of the cathode plate out to grippers, to an approximate angle of 15-20 degrees. The grippers then bring the copper to the horizontal position and pull it for separation.
However, if the metal that has deposited on the bottom edge of the cathode plate does not break during the initial stripping operation, it is necessary to flex the sheets upwardly and then downwardly until that metal breaks. Grippers are then used to flex the sheets of metal upwardly and downwardly until the interconnecting metal between the sheets breaks.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.
Throughout this specification, the term “comprising” and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicates otherwise.